That was the bubbling sounds of CalSpa at the Minnesota State Fair. CalSpa has been selling hot tubs at the Minnesota state fair for 18 years. Hot tubs are a staple of other state fairs, but CalSpa claims the Minnesota State Fair has the largest display of hot tubs in North America.MPR Photos/Nikki tundelView full galleryCalSpa markets to customers who are thinking about the onset of fall and wanting to invest in a warm winter activity. It's also a good place to snag couples who wouldn't otherwise drive to a hot tub show room.MPR Photos/Nikki Tundel